(WKBN) — The weather the past few days has featured sunny blue skies and warm temperatures. In fact, it has been hard to find a cloud in the sky this week. One of the exceptions is those little white streaks in the sky that are caused by airplanes.

What causes this phenomenon and why do some last longer than others? First, the scientific term for these white streaks is “condensation trail,” but they are typically referred to as “contrails.” You might know that contrails form due to the exhaust of aircraft, but did you know that there are multiple formation methods?

Method 1: Occurs when the hot and humid exhaust from aircraft mixes with low-temperature air that has low moisture content. The exhaust from the aircraft mixes with the cold air and eventually condenses into a cloud and thus the condensation trail is born. These contrails are what you typically see on a sunny and clear day.

Image of an airplane contrail over Binghamton, New York. Photo courtesy of the National Weather Service.

Method 2: The second method occurs when an aircraft flies through air that is clear but that has relative humidity near 100%. The pressure change caused by the airflow over the tip of the wing results in a reduction of air temperature and saturation of the air. The condensation usually occurs along the tips of the wing. This method of contrails is more rare compared to method #1.

Under the right weather conditions, contrails can persist for a long period of time similar to what we have seen over the Valley the past couple of days. Below is a picture taken by WKBN meteorologist Adam Clayton outside the WKBN studio on April 11, 2023.

Picture of airplane condensation trails outside of the WKBN studio in Boardman, Ohio.

History of contrails

Human flight is relatively new in human history and so is the formation of contrails. The first reports of contrails were from World War I when planes were finally able to reach high enough altitudes to produce condensation from exhaust.

Still, the formation of contrails was seldom studied until World War II when aerial battles became more common. One of the most pressing matters during the war was the detectability of aircraft. When the weather conditions were just right, pilots could use the contrail created by the aircraft to track the enemy plane down.

However, the formation of contrails caused issues for both sides. During especially heavy periods of aircraft combat, the clouds from contrails would become so thick that pilots had difficulty keeping track of friendly and enemy planes alike. These clouds made it difficult for planes to stay in formation and even caused collisions.

Due to the aforementioned issues, the study of contrails became important to the air forces of all sides in World War II. The Germans were able to first develop the now-accepted theory of contrail formation during World War II and then the United States arrived at the same conclusion independently after the war.

Presently, most of the research on contrails refers to the formation of clouds due to extensive air travel across the world. Specifically, most studies focus on how contrails can affect the amount of incoming/outgoing solar radiation into the Earth.